1. Field of the Invention
The invention is directed to a process for the manufacture of a metallic molded structural part for motor vehicle components which has areas with a higher ductility.
2. Description of the Related Art
Tool-heat-treated molded structural parts for motor vehicle components such as door impact girders or bumpers are manufactured with material characteristics which are distributed uniformly over the molded structural part. This is effected by means of a complete heat treatment of the molded structural parts. However, the ductility of the material decreases as a result of the high strength values achieved by the heat treatment with tensile strengths R.sub.m of approximately 1500 N/mm.sup.2. The material accordingly loses its capacity to deform in a permanent manner. The breaking elongation A.sub.5 is usually approximately 10%.
A varying plastic stiffness behavior of tool-heat-treated pressed molded structural parts is currently achieved by means of a partial rolling of the starting plates prior to shaping so that the thickness is reduced by area.
In different cases of application in automobile engineering, there is a need to provide areas with greater ductility in the molded structural parts. For this purpose, for example, closing plates, that is, inserts of softer steel quality, are integrated in the molded structural part. However, this procedure leads to a substantially more complicated manufacture and higher costs. Moreover, this adds appreciably to the weight of the molded structural part.
Also, the partial reduction in thickness using rolling technique to produce areas with different stiffness behavior entails high overhead and manufacturing costs. Further, depending on the configuration of the area to be rolled, the technological limits of processing by means of rolling techniques are restrictive. This is particularly true when rolling narrow regions.